1.Field of the Invention
This invention relates to fast electronic pulse processing, particularly in the context of pulsed X-ray fluorescence analysis using an energy-dispersive detector.
2. Description of the Prior Art
A major use of electronic pulse amplifiers is to amplify very small charge or voltage pulses from radiation detectors to a level where they may be processed to provide the required measurement data. The useful information in a pulse is usually contained in its amplitude and in its frequency (if periodic) or rate of arrival (if aperiodic). Random noise is always present. In one class of instruments (X-ray, gamma-ray and nuclear spectrometers, which may be generically referred to as emission spectroscopy systems), the rate of arrival of signal pulses can be high (for example, 10.sup.4 to 10.sup.6 pulses per second) and is usually random. The pulses have different heights and the output of the instrument is a histogram of the number of pulses in a given height interval against pulse height. The resolution of the detector (e.g., a solid-state detector) used in such a system can be such that the width of a useful pulse height interval must be less than 0.1% of the maximum pulse height being processed.
The conventional electronic techniques for amplifying these pulses with respect to detector speed have been painfully slow and far below the capacity of certain types of detectors (e.g., a solid-state detector) to produce meaningful energy charges. Attempts to speed up such amplification have resulted in distorting the pulses significantly with respect to detector resolution. Present solid-state radiation detectors have nanosecond response times. State-of-the-art filtering systems for analyzing charges develop analog pulses having durations on the order of 60-70 microseconds. Faster filtering is not possible without introducing significant noise. The dead time existing in this pulse period is the major limiting factor in the processing of pulses in the solid-state radiation spectrometer and such period cannot be materially reduced even with the best possible analog filter. Hence, a fundamentally new approach to treating pulses is needed to improve the operating speed. The theory, to be hereinafter explained more fully, does away with attempting to improve the filtering of an analog pulse. Instead, the theory provides for deducing the peak value from certain sampled data leading up to the peak and additional sampled data following the peak, all of which is treated digitally, thereby avoiding having to use an analog filter.
Therefore, it is a feature of this invention to provide an improved method of processing charges resulting from an energy-dispersive, solid-state detector used in an emission spectroscopy system so that the operating speed is superior to that achievable by analog filtering for the same resolution.
It is still another feature of this invention to provide an improved system of processing rapidly occurring pulses in the context of an energy-dispersive, solid-state detector by using a source controlled by the detector electronics to essentially eliminate the "dead-time" portion of the pulse periods.
It is yet another feature of this invention to provide an improved system of processing rapidly occurring pulses in the context of an energy-dispersive, solid-state detector by using a pulsed source whose switch-on and switch-off times are controlled by the detector electronics to essentially eliminate the "dead-time" portion of the periods of the pulses being processed.